A Histochemical and Electron Microscopic Analysis of the Spiculogenesis in the Demosponge Suberites domuncula

Carsten Eckert ¹, Heinz C. Schröder ¹, David Brandt ¹, Sanja Perovic-Ottstadt ¹ and Werner E.G. Müller ^1*

¹ Museum für Naturkunde, Universität, Institut für Systematische Zoologie, Berlin, Germany (CE), and Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Mainz, Germany (HCS,DB,SP-O,WEGM)

^* To whom correspondence should be addressed. E-mail: wmueller{at}uni-mainz.de.

Submitted on December 17, 2005
Accepted on 24 April 2006

	Abstract

The skeleton of demosponges is built of spicules, which consist of biosilica. By use of the primmorph system from Suberites domuncula we demonstrate that silicatein, the biosilica-synthesizing enzyme, and silicase, the catabolic enzyme, are colocalized at the surface of growing spicules as well as in the axial filament, which is located in the axial canal. It is assumed that these two enzymes are responsible for the deposition of biosilica. In search of additional potential structural molecules, which might guide the mineralization process during spiculogenesis to species-specific spicules, electron microscopic studies with antibodies against galectin and silicatein were performed. These studies showed that silicatein forms a complex with galectin; the strings/bundles of this complex are intimately associated with the surface of the spicules and arranged concentrically around them. The collagen fibers are near the silactein/galectin complexes. The strings/bundles formed from silicatein/galectin display a lower degree of orientation than the collagen fibers which are arranged in a highly ordered pattern around the spicules. These data indicate that species-specific formation of spicules involves a network of (diffusible) regulatory factor(s) controlling enzymatic silica deposition; this mineralization process proceeds on a galectin/collagen organic matrix.

Key Words: sponges, porifera, Suberites domuncula, spicules, biosilica, silicatein, silicase, collagen, galectin

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